The present invention relates to a semiconductor device, and more particularly to a semiconductor device using a material having a high dielectric constant.
With the progressive microminiaturization of components in semiconductor devices, of late it has been required that the gate of a transistor should be 0.15 μm in length and the gate dielectric film, if formed by SiO2, for example, should be made as thin as 2 nm or less in thickness.
With dielectric films having such a thin thickness, a tunneling current that passes through them is so large as not to be negligible. A possible solution to this problem has been considered to increase the physical thickness of the dielectric film while maintaining the dielectric properties by using a dielectric material having a higher dielectric constant than that of SiO2. Materials regarded as candidates for the above-mentioned material with high dielectric constant are zirconium oxide or hafnium oxide as is described in the 2000, February issue (pp.93-106) of Nikkei Microdevices, for example. However, zirconium oxide or hafnium oxide forms a layer of reaction compound with a thickness of about 1.5 nm˜2.5 nm at the interface with the silicon substrate as stated in the lecture papers (Lecture No. 6.1, pp. 99-133, and Lecture No. 6.4, pp. 145-148) of 1999 IEEE (THE INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS) INTERNATIONAL ELECTRON DEVICES MEETING, for example.
Such reaction compounds are likely to degrade electrical characteristics.